Í desember sendum við ekki bara bréf, heldur líka litlar gjafir til vina okkar.

Í desember means in December.

Here, í is the preposition in, and with expressions of time like months it commonly takes the dative in Icelandic. The noun desember therefore appears in its dative form here.

So:

• í desember = in December

This is a very common way to talk about months and time periods.

This is because Icelandic normally follows a verb-second pattern in main clauses.

That means the finite verb usually comes in the second position in the sentence. If you begin with a time phrase like Í desember, then the verb comes next, and the subject follows after it.

So the structure is:

• Í desember = first element
• sendum = finite verb in second position
• við = subject

Compare:

• Við sendum ... = We send ...
• Í desember sendum við ... = In December, we send ...

Both are normal, but the second one emphasizes the time.

Sendum is the verb to send in the present tense, 1st person plural.

So:

• að senda = to send
• við sendum = we send

In this sentence, við means we.

Because of the word order, the verb appears before the subject, but it still means we send.

This is a very common Icelandic pattern meaning:

• not only ..., but also ...

So:

• ekki bara bréf = not just letters
• heldur líka litlar gjafir = but also small gifts

A very literal breakdown is:

• ekki = not
• bara = just / only
• heldur = but rather / but
• líka = also

Together, the phrase works like English not only X, but also Y.

Here bréf means letters, so it is plural in meaning.

The tricky part is that bréf is one of those Icelandic neuter nouns whose singular and plural can look the same in the nominative and accusative.

So:

• bréf = a letter
• bréf = letters

You tell the difference from the context. In this sentence, it is understood as plural because the meaning is we send not just letters, but also small gifts.

Litlar gjafir means small gifts.

The noun gjöf is feminine, and here it is in the plural accusative, because it is a direct object of sendum.

The adjective lítill = small must agree with the noun in:

• gender
• number
• case

So:

• gjafir = feminine plural accusative
• litlar = matching feminine plural accusative adjective form

That is why you get:

• litlar gjafir

They are the direct objects of the verb að senda.

In Icelandic, the thing being sent is typically put in the accusative:

• send letters
• send gifts

So in this sentence:

• bréf = direct object
• litlar gjafir = direct object

That is why those noun phrases are in the accusative.

Til vina okkar means to our friends.

The important grammar point is that the preposition til takes the genitive case. So the noun after it must be in the genitive.

That gives:

• til
  • genitive
• vinir = friends in the basic plural form
• vina = of friends / to friends after til

So:

• til vina okkar = to our friends

Because til requires the genitive, not the dative.

Compare:

• vina = genitive plural
• vinum = dative plural

Since the sentence has til, the correct form is:

• til vina

not:

• til vinum

This is something learners need to memorize with prepositions: different prepositions require different cases.

Okkar means our, but grammatically it is the genitive form of við = we.

In Icelandic, possessive words like this often come after the noun:

• vinir okkar = our friends

Because til requires the genitive, the whole phrase becomes:

• til vina okkar

Here:

• vina = genitive plural of vinur
• okkar = our

So the meaning is simply to our friends.

Icelandic often leaves nouns indefinite without any extra word.

So:

• bréf can mean letters
• litlar gjafir can mean small gifts

English often needs something like the, some, or a/an, but Icelandic does not always express that in the same way.

In this sentence, the nouns are just presented in a general indefinite sense:

• we send letters
• we send small gifts

Often yes, but not always mechanically.

In this sentence, ekki bara ... heldur líka ... works as a fixed pattern meaning:

• not only ..., but also ...

So here bara is part of that larger expression, not just a standalone only.

If you translate word by word, you get something like:

• not just letters, but also small gifts

That is very close to the real meaning.

Sometimes heldur can have a rather / instead kind of sense, but in this sentence it is best understood as part of the pair:

• ekki bara ..., heldur líka ...

So here you should learn it as part of the whole construction:

• not only ..., but also ...

That will help you more than trying to translate heldur by itself.